Device for automatically varying the stitch length in a zig-zag sewing machine



3,426,709 CH LENGTH IN Feb. 11, 1969 EJJlNDIlCH ETAL DEVICE FOR AUTOMATICALLY VARYING THE STIT A ZIG-ZAG SEWING MACHINE Filed Jan.

Sheet Feb. 11,1969

3,426,709 TH IN E. JINDRTICH ET AL ATI DEVICE FOR AUTOM CALLY VARYING THE STITCH LENG A ZIG-ZAG SEWING MACHINE Filed Jan. 1.6, 1967 Sheet INVENTORS Z m //70/ /(fi a n/177K616 BY I fiq lek W W airy United States Patent 3,426,709 DEVICE FOR AUTOMATICALLY VARYING THE STITCH LENGTH IN A ZlG-ZAG EW- ING MACHINE Emil Jindrich and Frantisek Bajer, Prostejov, Czechoslovakia, assignors to Elitex, Zavody Textilniho Strojirenstvi, Generalni Reditelstvi, Liherec, Czechoslovakia Filed Jan. 16, 1967, Ser. No. 609,552 Claims priority, application Czechoslovakia, .Fan. 19, 1966, 321/ 66 US. Cl. 112-73 5 Claims Int. Cl. D05]: 3/06, 3/02 ABSTRACT OF THE DISGLQSURE A control device for automatically varying the stitch length in a zig-Zag buttonhole sewing machine Which automatically forms barring stitches and covering stitches at the narrow end of the buttonhole has a mechanism for turning the plane of needle bar oscillation during the forming of the barring stitches, and provisions for manually varying the stitch length. The device includes a linkage between the needle bar turning mechanism and the stitch length varying arrangement for operating the latter automatically in response to the turning of the needle bar by the former.

Background of the invention Known automatic buttonhole seing machines form a seam of zig-zag two-thread chain stitches about a keyhole-shaped opening in a piece of material, usually fabric. It was known heretofore to finish the narrow end of the keyhole-shaped seam on a second sewing machine by forming a row of barring stitches across the straight ends of the keyhole seam for reinforcing the fabric and preventing enlargement of the buttonhole by tearing of the fabric, and thereafter to overlay the barring stitches with covering stitches for better appearance.

In our simultaneously filed application Ser. No. 609,569, we have disclosed and claimed a buttonhole sewing machine which automatically forms barring and covering stitches at the narrow end of the keyhole seam from the same threads and on the same machine employed for making the keyhole seam.

As is customary in zig-zag sewing machines, the machine of our copending application oscillates the needle bar in a plane passing aproximately through the longitudinal axis of the bar. In forming the barring stitches, the plane of oscillation of the needle bar is turned approxi mately about the needle axis through an angle of 90, and the covering stitches formed thereafter are at right angles to the stitches in the straight end portions of the keyhole seam.

In its basic aspects, the aforedescribed machine normally forms stitches of uniform length. While it is known manually to adjust the stitch length in zig-zag saw machines, such manual adjustment is not practical during the operation of an automatic buttonhole sewing machine. The barring stitches and covering stitches Produced are therefore as wide as the stitches which form the keyhole seam. A relatively great width of the barring and covering seams is neither necessary for preventing tearing of the fabric at the narrow end of the buttonhole, nor does a wide covering seam look attractive.

Summary of the invention The invention provides a device which automatically changes the length or amplitude of the zigzag stitches after completion of the keyhole seam and during formation of the barring stitches so that the latter become gradually shorter, and the covering stitches subsequently 3,426,709 Patented Feb. 11, 1969 Other features and many of the attendant advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of a preferred embodiment when considered in connection with the accompanying drawings in which:

FIG. 1 shows the stitch-length controlling mechanism of the invention and as much of the buttonhole sewing machine of the copending application referred to above as is necessary for an understanding of this invention in a perspective view;

FIG. 2 diagrammatically illustrates the motions of some stitch-controlling elements of the apparatus of FIG. 1; and

FIG. 3 shows the stitch pattern of a buttonhole sewn on the machine partly illustrated in FIG. 1.

Description of the preferred embodiment FIG. 1 shows elements of the buttonhole sewing machine of the aforementioned, simultaneously filed application whose reference numerals are between 0 and 199, and elements also found in other buttonhole sewing machines in which the stitch length can be controlled by hand, such known elements being numbered 200 to 299. The parts of the apparatus which are characteristic of this invention are numbered 300 and higher.

The elements of our other invention illustrated in FIG. 1 include a plate cam 19 which has an external gear rim and is driven by the sewing machine motor through a non-illustrated gear train and clutches in proper synchronization with the other sewing machine elements during formation of the keyhole seam. The radial face of the cam 19, not visible in FIG. 1, carries a cam track which controls movement of a work table and of a workpiece held on the table past the needle 239 of the sewing machine in the direction of buttonhole elongation.

The cam 19 is rotatably mounted on a vertical shaft 20 journaled in the sewing machine head by means of a bearing and in the machine base in a bearing 91. The shaft 20 drives a gripper or looper in the base in a conventional manner, not shown. Power is transmitted from the nonillustrated drive motor of the sewing machine to the shaft 20 by a drive shaft 49 journaled in the machine head at 50 and meshing bevel gears 88, 90. The drive shaft is connected by a non-illustrated, conventional system of cams and levers with the needle bar 234 of the sewing machine for moving the needle 239 up and down transversely of the supporting surface of the non-illustrated work table and of a workpiece held thereon.

The needle bar 234 is oscillated about a horizontal axis, as is necessary in the formation of zig-zag stitches on a non-oscillating workpiece by a mechanism including a lever 203 having a pivot bearing 204 in which a pivot pin 205 is rotatably received. The pin is mounted on a slide 206 movably received in a slot 207 of a guide frame 208 for movement of the slide'and of the pin in the direction of the arrows A, B. The frame is attached to a shaft 209 movably received in a bearing 210 of the sewing machine head.

The lever 203 is oscillated about the pin 205 by an eccentric 201 on the drive shaft 49 which is received in a fork 202 on one end of the lever 203. The other end of the lever is provided with an eye 216' which rotatably receives a pin 217 on an arm 218 attached to a shaft 219.

The shaft is journaled in the machine head at 220, and a guide passage 221 in the shaft receives the stem 222 of a fork 223 for sliding movement transverse to the shaft axis. The free ends 224 of the fork 23 rotatably receive coaxial pins 226 which extend in diametrically opposite directions from a ring 225 axially secured on a cylindrical guide tube 227 by a collar 233, but rotatable about the tube axis. The needle bar 234 is coaxially slidable in the tube 227, and is also guided in a universal joint 235 which permits longitudinal movement and angular displacement of the bar.

An approximately cubical slide 228 is attached to the lower end of the guide tube 227 and is provided with approximately diagonal grooves 229 in two opposite faces parallel to the needle bar axis. The grooves are parallel to each other and obliquely inclined relative to the direction of needle bar movement. They are cammingly engaged by pins 230 on respective dependent brackets 231 on a gear 110 which is secured in the sewing machine head against axial displacement and against translatory movement transverse of its axis in a known manner, not further illustrated. The gear 110 has a central aperture 232 in which the guide tube 227 is received with ample radial clearance to permit the necessary swinging movement of the needle 239.

When the eccentric 201 turns in the fork 202, the lever 203 not only pivots on the pin 205, but also moves longitudinally and displaces the pin and the attached slide 206 along the slot 207 (see FIG. 2). The positions of the device in the two terminal positions of the fork 202 during each revolution of the eccentric 201 are indicated in fully drawn and in broken lines, respectively.

The path of the pin 205 in the guide frame 208 is obliquely inclined relative to a line p perpendicular to the length of the lever 203 in the position shown in broken lines. The magnitude of the longitudinal lever displacement y is a function of the angle 7 enclosed by the line p and the direction of pin movement in the slot 207, and is identical with the stroke of the pin 217 on the arm 218.

The amplitude of angular oscillation of the fork 223 can thus be changed by adjusting the angular position of the frame 208 relative to the axis of the shaft 209, and the vertical stroke of oscillating movement of the guide tube 227 is correspondingly changed. The pins 230' being axially secured relative to the guide tube 227. a change in the vertical stroke of the tube brings about an amplitude change in the horizontal oscillating movement of the needle 239 about the common axis of the pins 226, and a change in the stitch length.

The frame 208 carries a cam follower 211 which is held against an approximately helical face of a radial cam 212 by a tension spring 216. When the cam 212 is turned by means of a knob 215 mounted on a common shaft 213 with the cam and journaled in the machine head at 214, the cam follower 211 is moved in a horizontal direction to pivot the frame 208 about the axis of the shaft 209. The amplitude of the swinging movement of the needle 239 in an axial plane, and the resulting length of the zig-zag stitches formed by the cooperation of the needle 239 with the non-illustrated gripper or looper mechanism may thus be set by turning the knob 215 which carries indicia calibrated in suitable units of stitch length.

With the exceptions identified by reference numerals smaller than 200, the structure described above is conventional, and its operation is known.

The radial face of the cam plate 19 visible in FIG. 1 has a groove 236 which provides a cam track for a cam follower 96 rotatably mounted on a rocker 98 by means of a pin 97. The pin is adjustably secured in a slot 238 in the longer arm of the rocker which swings in the sewing machine base about a vertical pin 99 fastened in the stationary sewing machine structure during formation of the bight portion of the keyhole seam. As is more fully explained in our copending application, the rocker 98 is pivoted on the pin 99 by a radial cam 151 engaging the shorter arm 155 of the rocker 98 during the formation of a row of barring stitches across the narrow end of the buttonhole. The cam follower 96 is free to move in an enlarged portion 237 of the cam track 236 during the cooperation of the rocker 98 with the cam 151.

Hinges 101, 103 and an interposed link 102 connect the longer arm of the rocker 98 with a radial arm 104 on a vertical shaft 105 journaled in the sewing machine head at 106 and in the machine base at 107. The shaft carries a segment 108 which meshingly engages the gear 110, and another segment 109 which similarly engages a gear 111 of the gripper mechanism, not otherwise shown. When the shaft 105 is turned by the rocker 98, the cubical slide 228 and the gripper mechanism are turned about the vertical axis which is common to the needle mechanism and the gripper mechanism in the center of their oscillating motions, and the plane of oscillating movement is turned correspondingly. When the shaft 105 turns while the sewing implements operate, the consecutive zig-zag stitches formed are angularly offset from each other.

The sewing implements are turned by means of the cam 151 during formation of barring stitches on a buttonhole in the machine of our copending application. The length of the barring stitches and of covering stitches subsequently laid over the barring stitches in that machine is identical with the length of the zig-zag stitches formed about the keyhole-shaped circumference of the buttonhole. The seam formed across the narrow end of the buttonhole to prevent tearing of the fabric at that end is therefore relatively wide, and wider than is necessary for accomplishing the desired fabric reinforcement, and wider than is desirable from the point of view of appearance.

It would be possible, but obviously impractical, to reduce the stitch length by turning the knob 215 when sewing of each keyhole seam is completed, and when sewing of the barring and covering stitches is automatically started by the machine of our copending application. The present invention, in its more specific aspects, provides an automatic gradual reduction of the stitch length during formation of the barring stitches, and maintains the stitch length at a minimum value during the sewing of a row of covering stitches at right angles to the straight portions of the keyhole seam.

A collar 307 is rotatably mounted on the top end of the shaft 105 and may be secured in a desired angular position on the shaft by a set screw 310. An abutment pin 308 radially projects from the collar 307. A guide pin 309 coaxially projects from the top of the shaft 105.

The shaft 209 is provided with a radial arm 301 to which one end of a sheet metal link 303 is attached by a pivot pin 302. The other end of the link 303 has a transverse abutment edge 306 and an integral, approximately horizontal flange 304 in whose longitudinal slot 305 the pin 309 is slidably received.

While the sewing implements are turned during formation of the barring stitches by angular movement of the shaft 105 and if the collar 307 is originally set as shown in FIG. 1, the pin 308 abuttingly engages the edge 306 after the shaft 105 has moved through a small angle. The pin thereafter gradually shifts the link 303 in the direction of the arrow H and thereby pivots the arm 301 and the frame 208 in the direction of the arrow B, whereby the cam follower 211 is lifted from the cam 212.

It will be appreciated that the pin 308 approaches the engaging position during sewing of the bight portion of the keyhole seam in a direction toward the edge 306, that is, counterclockwise as viewed from above, so that the stitch-shortening mechanism of the invention is ineffective during sewing of the keyhole seam.

When the shaft 105 is gradually turned during formation of barring stitches on an otherwise completed keyhole seam, the barring stitches are angularly offset relative to each other and become gradually shorter so that the last barring stitch, which is approximately perpendicular to the first barring stitch, may have a length of only one-half or one-third of the length of the first barring stitch or of the length of the zig-zag stitches in the keyhole seam. When a row of covering stitches is subsequently laid over the barring stitches while the cam follower 96 travels along a circular portion of the cam track 236 and the shaft 105 stands still, the covering stitches have the same width as the last barring stitches.

The appearance of a keyhole seam produced on the sewing machine of this invention is evident from FIG. 3, wherein relatively wide zig-zag stitches 311 extend in a keyhole pattern having two straight and parallel portions 312 connected by an enlarged bight portion 313. The free ends of the parallel portions 312 are connected by a transverse row of covering stitches 314 made integrally of the same threads as the keyhole seam, but of greatly reduced uniform length. The short covering stitches conceal the barring stitches in the view of FIG. 3.

When the covering stitches are completed, the cam 151 swings the shaft 105 against the direction of the arrow G until the sewing implements are positioned for sewing a straight portion 312 of another keyhole seam. Simultaneously, the pin 308 is swung in a direction away from the pin 302, permitting the frame 208 to swing in the direction of the arrow F until the cam follower 211 abuts against the cam 212 and the machine is set for sewing the wider stitches of the keyhole seam which may be adjusted for a series of keyholes or for individual keyholes by turning the knot 215. The width of the barring and covering stitches may be adjusted similarly by loosening the set screw 310, angnllarly shifting the collar 307 on the shaft 105, and again tightening the screw 310.

At this time, we do not foresee a need for a row of barring stitches and covering stitches of greater length than the stitches of the associated keyhole, but it will be appreciated that such longer barring stitches and covering stitches can be produced on the illustrated and described apparatus after a simple modification in which the flange 304 is bent 180 about the longitudinal axis of the link 303 and the collar 306 is shifted 180 on the shaft 105 from the illustrated position so that the pin 308 permits the frame 108 to be shifted in the direction of the arrow B by the spring 216 when the shaft 105 turns in the direction of the arrow G, and holds the frame in the illustrated position during sewing of the keyhole seam.

It should be understood, of course, that the foregoing disclosure relates only to a preferred embodiment of the invention, and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not depart from the scope and spirit of the invention defined in the appended claims.

We claim:

1. In a zig-zag sewing machine, in combination:

(a) a needle bar having an axis and being axially movable toward and away from a work piece;

(b) oscillating means for oscillating said needle bar in a plane extending through to said axis;

(c) turning means operable for turning said plane of oscillation substantially about said axis; and

(d) stitch length-control means operatively connected to said oscillating means and to said turn means for simultaneously progressively increasing the amplitude of said oscillations to a predetermined amplitude in response to the turning of said plane by said turning means in one direction and maintaining said increased amplitude while said turning means is inoperative, and for simultaneously progressively decreasing the amplitude of said oscillations to a predetermined amplitude in response to the turning of said plane by said turning means in a direction opposite to said one direction and maintaining said decreased amplitude while said turning means is inoperative.

2. In a machine as set forth in claim 1, said oscillating means including an elongated link member (203) having a plurality of longitudinal portions (202, 204, 216'); a rotatable shaft member (219); an arm (218) having one end attached to said shaft member for arcuate movement of another end of said arm about said shaft when the shaft rotates; pivot means (217) pivotally connecting said other end of said arm to a first longitudinal portion (216') of said link member; guide means (206, 208) for guiding a second longitudinal portion (204) of said link member in a path obliquely inclined relative to the direction of elongation of said link member; means (201) for oscillating a third longitudinal portion (202) of said link member transversely of said direction of elongation; and motion transmitting means (213, 235) connecting said shaft to said needle bar (234) for oscillating the same in response to cyclic rotary motion of said shaft; said control means including means (303, 308) for varying the angle of inclination of said path relative to said direction of elongation in response to said turning means.

3. In a machine as set forth in claim 2, said second longitudinal portion (204) being spacedly interposed between said first and second longitudinal portion (216', 202).

4. In a machine as set forth in claim 2, said guide means including a guide member (208) defining an elongated guide slot (207), and engaging means (205) fast on said second portion (204) and longitudinally slidable in said slot; and said control means including means (303, 308) for moving said guide member between a plurality of positions in which the directions of elongation of said slot and of said link members define said angle of inclination.

5. In a machine as set forth in claim 1, abutment means (211, 212) for limiting turning of said plane in one of said directions.

References Cited UNITED STATES PATENTS 738,591 9/1903 Allen 11273 1,770,862 7/1930 Ritchie 112- 2,411,493 11/1946 Wood 112-73 JORDAN FRANKLIN, Primary Examiner.

H. HAMPTON HUNTER, Assistant Examiner.

U.S. Cl. X.R. 112158 

